Hydrogen purification

ABSTRACT

An improved apparatus and process for the removal of gaseous impurities from an impure gas stream of hydrogen contaminated with carbon monoxide, and with one or more additional impurities such as carbon dioxide, oxygen, nitrogen, water, methane. 
     The impure gas stream is first contacted with elemental nickel in a first reaction zone under nickel-carbonyl forming conditions thereby converting substantially all the carbon monoxide to nickel carbonyl, thereby producing a partially purified gas stream. 
     The partially purified gas stream is then contacted with Ti 2 Ni or certain manganese-containing alloys in a second reaction zone to produce a fully purified gas stream.

This is a continuation of application Ser. No. 08/456,714 Jun. 1, 1995abandoned which is a continuation of U.S. patent application Ser. No.08/230,707, filed Apr. 21, 1994 U.S. Pat. No. 5,492,682.

BACKGROUND

This invention relates in general to hydrogen purification by which ismeant an improved process for the removal of gaseous impurities from animpure gas stream of hydrogen contaminated with carbon monoxide, andwith one or more additional impurities. The additional impurities can becarbon dioxide, oxygen, nitrogen, water, and/or methane. Methane isfrequently present in commercially available impure hydrogen at a levelof 5 parts per million (ppm) which is 5,000 parts per billion (ppb).Methane can also be formed in situ by the reaction of the hydrogen withthe carbon monoxide and or carbon dioxide. Methane formation is avoidedin this new improved process. This process can be employed to purifyimpure hydrogen such that the resultant purified gas contains less than50 ppb or even less than 20 ppb of methane i.e. less than 20 parts byvolume of methane per 1,000,000,000 parts by volume of hydrogen.

The semiconductor industry is developing integrated circuits with evermore increasing line densities requiring that the materials used in themanufacturing process be of ever increasing purity. As hydrogen is oneof the gases used in these processes, it must be as pure as possible.The impurities present in commercially available hydrogen include:carbon monoxide, and one or more additional impurities. The additionalimpurities can be carbon dioxide, oxygen, nitrogen, water, and/ormethane.

One prior method for the purification of impure hydrogen is theselective diffusion of hydrogen through palladium or palladium alloys asdescribed for example in U.S. Pat. No. 3,534,531. Such processes suffersfrom a number of disadvantages. Unfortunately the rate of diffusionincreases with the pressure drop across the sides of the palladiumbarrier. Another disadvantage is the requirement for a high operatingtemperature in order to achieve an economical throughput. Furthermore,as the impurities are blocked by the palladium barrier, a removal devicemust be provided. Such a removal device is described in U.S. Pat. No.3,368,329. Removal devices are expensive to acquire and costly tomaintain. Another disadvantage is the propensity of the palladiumbarrier to rupture with consequent leakage of impurities into thepurified gas stream. This propensity is all the more prevalent becauseof the incentive to make the palladium barrier thin and to increase thedifferential pressure in order to increase the throughput. The use ofhigh-temperature, high-pressure hydrogen is dangerous because of itspropensity to explosively, exothermically combine with atmosphericoxygen. Finally palladium is expensive.

SUMMARY OF THE INVENTION

Accordingly it is an object of the present invention to provide animproved process for the purification of impure hydrogen substantiallyfree of one or more of the disadvantages of prior process for thepurification of impure hydrogens.

Another object is to provide an improved process for the purification ofimpure hydrogen which does not require the use of either palladium orits alloys or its compounds.

Another object is to provide an improved process for the purification ofimpure hydrogen which does not require the use of a diffusion membrane.

Another object is to provide an improved process for the purification ofimpure hydrogen which does not require the heating of the impurehydrogen.

Another object is to provide an improved process for the purification ofimpure hydrogen which does not require the use of hydrogen underpressure.

Another object is to provide an improved process for the purification ofimpure hydrogen which avoids the production of methane by the reactionof the hydrogen with either the carbon monoxide or the carbon dioxidewhich is present.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects are accomplished by providing an improvedprocess for the purification of impure hydrogen as described in thefollowing description and drawings wherein:

FIG. 1 is a schematic view of an apparatus capable of practicing theimproved process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention there is provided: an improvedprocess for the removal of gaseous impurities from an impure gas streamof hydrogen contaminated with carbon monoxide, and with one or moreadditional impurities. These impurities are carbon dioxide, oxygen,nitrogen, water, and/or methane, and mixtures thereof. The processcomprises the steps of:

I. contacting the impure gas stream with elemental nickel in a firstreaction zone under nickel-carbonyl forming conditions therebyconverting substantially all the carbon monoxide to nickel carbonyl, toproduce a partially purified gas stream; and then

II. contacting the partially purified gas stream with Ti₂Ni in a secondreaction zone under reacting conditions to produce a fully purified gasstream.

In another embodiment of the present invention the Ti₂Ni is replacedwith an alloy of Ti, V, Fe, and Mn wherein: (a) the weight ratio of Ti:Vis from about 1:100 to about 100:1; (b) the weight ratio of Ti:Fe isfrom about 1:100 to about 100:1; and (c) the weight ratio of Ti:Mn isfrom about 1:100 to about 100:1.

The pressure in both Step I arid Step II is generally from about 1 toabout 20 bar.

The temperature in Step II is generally from about 400 to 600° C. and ispreferably from about 500 to about 600° C.

The elemental nickel, and the nickel compounds such as nickel oxide ifpresent, can be employed unsupported but is preferably supported on acarrier having a surface area generally greater than 100 and preferablygreater than 200 square meters per gram of weight based on the weight ofthe carrier.

A wide variety of carriers can be employed for the nickel, but ispreferably of silicalite, titanium silicalite and silica as described inU.S. Pat. No. 4,713,224, and xerogel as shown in EP-A-537851.

The nickel containing bed can be followed or proceeded by a sorbing bedconsisting essentially of a natural or synthetic molecular sieve; inalternative the nickel bed can be interposed between two molecular sievebeds. Examples of such molecular sieves include natural or syntheticzeolites, silicalites or titanium silicalites.

The second reaction zone can be of any form but is preferably a housingwith uniformly polished inner walls having a roughness expressed incenterline average height less than 0.5 microns and preferably less than0.25 microns.

A wide variety of gas stream velocities can be employed but thepartially purified gas stream in Step II preferably has a velocity offrom about 0.5 to about 50 cubic centimeters per minute per gram ofTi₂Ni or per gram of alloy when measured at a pressure of 760 mm Hg and20° C.

The Ti₂Ni and the alloy is preferably in the form of a loose powderhaving an average particle size of from about 1 to about 500 microns andpreferably from about 1 to about 250 microns. In one embodiment thispowder can advantageously be pressed to form pellets having a diameterfrom about 0.5 to about 5 mm.

Shaping into pellets can be carried out by compression of by sintering.Sintering can be by heating of the powder alone or in combination with asecond powder as described in GB Patent Publication No. 2,077,487 inorder to reach a satisfactory level of porosity. The resultant pelletsgenerally have a diameter of from about 0.5 to 5 mm.

According to another aspect of the present invention there is providedan improved apparatus for the removal of gaseous impurities from theabove-described impure gas stream of hydrogen. The apparatus comprises:

A. a first reaction zone containing elemental nickel; and

B. the impure gas stream; and

C. means for conveying the impure gas stream to the first reaction zone;and

D. means for maintaining said first reaction zone under nickel-carbonylforming conditions thereby converting substantially all the carbonmonoxide to nickel carbonyl, thereby producing an effluent stream formthe first zone which effluent stream is a partially purified gas stream;and

E. a second zone containing either the Ti₂Ni or the alloy; and

F. means for conveying the partially purified gas stream from the firstzone to the second reaction zone; and

G. means for maintaining the second reaction zone under methane reactingconditions to produce a fully purified gas stream.

Referring now to the single figure of the drawing there is shown apurifier 100 for the removal of impurities from an impurity-containinggas stream. The purifier 100 has a gas inlet 102 in fluid communicationthrough pipes 104, 104′ with a preliminary chambers 106, 106′. Valves108, 108′ can be alternately opened or closed to allow the passage ofthe impurity-containing gas through the first or the second of thepreliminary purification chambers 106, 106′ containing a bed ofparticulate material 110, based on supported nickel whereby the bedremoves, at a relatively low temperature, the relatively easilyremovable impurities such as carbon monoxide and carbon dioxide.Chambers 106, 106′ may in addition contain a natural or syntheticmolecular sieve 111 to better promote the removal of carbon dioxide, oralternatively a separate molecular sieve can be provided. The chambers106, 106′ can also remove moisture down to trace levels, but do notremove nitrogen or methane.

In accordance with the present invention it is possible to obtain apartially purified hydrogen-gas-mixture containing only a second classof impurities which are nitrogen and methane. The partially purifiedgas-mixture leaves preliminary purification chambers 106, 106′ enteringa final purification chamber 112, kept at a much higher temperature withwhich chambers 106, 106′ are in fluid communication, by means of pipes114, 114′. Valves 116, 116′ control the flow of the partially purifiedgas from either of the first preliminary purification chambers 106,106′, which allows the regeneration of nickel in one chamber while theother chamber is working. In said final purification chamber 112, thepartially purified hydrogen comes in contact with a bed of material 118.

The invention will be understood by the following examples wherein allparts and percentages are by weight unless otherwise indicated. Theseexamples are designed to teach those skilled in the art how to practicethe present invention and represent the best mode presently known forcarrying out the present invention.

EXAMPLE 1

This example illustrates a preferred embodiment of the present inventionemploying Ti₂Ni.

An impure gas stream contaminated with 5000 parts per billion (“ppb”) ofmethane, traces of nitrogen, traces of CO₂, traces of CO, balancehydrogen was allowed to flow at a rate of 100 cc/min at a pressure of 4bar at room temperature into a first reaction zone in a chamber 106containing two beds of sorbing material. Upstream is a bed 111 ofsynthetic zeolite. Downstream is a bed 110 containing 20 grams of acertain nickel catalyst. The nickel catalyst contains 58% by weightatomic nickel. Of the entire amount Of the atomic nickel, 5% by weightis elemental metallic nickel and 95% by weight is in the form of nickeloxide. The nickel is supported on a silica carrier. The catalyst has asurface area of about 100 square meters per gram. This catalyst is soldby the Engelhardt company under the trade name “Ni 0104T”. It can beseen that in the first reaction zone the impure gas stream is contactedwith elemental nickel under nickel-carbonyl forming conditions therebyconverting substantially all the carbon monoxide to nickel carbonyl, toproduce a partially purified gas stream. This partially purified gasstream is free of even the traces of CO present in the original gas. Theamount of CO if present is so low as to be unmeasurable.

The partially purified gas stream is then lead to a in a second reactionzone where it is contacted with 40 grams Ti₂Ni at 550° C. produce afully purified gas stream free of methane, free of CO and free of CO₂.The Ti₂Ni is in the form of a loose powder having an average particlesize of from one to 150 microns.

The level of methane was measured at the outlet of the second zone bymeans of a Valco gas chromatograph employing a metastable heliumionization detector having a sensitivity of 5 ppb of methane. At thebeginning of the test no methane could be detected, apparently becausethe fresh Ti₂Ni was sorbing all the methane. At a certain later point intime a trace of methane was detected. The test was arrested when themethane level increased to 50 ppb. From the elapsed time it wascalculated that greater than about 1.36 liter-torr of methane per gramof Ti₂Ni had been sorbed. This value is reported in Table 1 as sorptioncapacity.

EXAMPLE 2

This example illustrates another preferred embodiment of the presentinvention employing a getter alloy having a small amount of manganese.

The procedure of Example 1 is repeated except that the Ti₂Ni is replacedby a getter alloy having the following composition: 56.7% Ti; 30.2% V;6.6% Fe; 6.5% Mn. This alloy contains 6.5% by weight manganese and isreferred to below as “low Mn alloy”. The sorption capacity is measuredand is reported in Table 1.

EXAMPLE 3

This example illustrates a preferred embodiment of the present inventionemploying a getter alloy having a high amount of manganese.

The procedure of Example 1 is repeated except that the Ti₂Ni is replacedby a getter alloy having the following composition: 30.1% Ti; 14.4% V;10.5% Fe; 44.9% Mn. This alloy contains 44.9% by weight manganese and isreferred to below as “high Mn alloy”. The sorption capacity is measuredand is reported in table 1.

TABLE 1 Example Sorption Capacity No. Getter material (Liter-torr/gm) 1Ti₂Ni 1.36 2 Low Mn alloy 0.96 3 High Mn alloy 1.22

Although the invention has been described in considerable detail withrespect to certain preferred embodiments thereof, it will be understoodthat variations are within the skill of the art without departing fromthe spirit of the invention as described above and as defined in theappended claims.

What is claimed is:
 1. An apparatus for the removal of gaseousimpurities from an impure hydrogen gas stream contaminated with carbonmonoxide, and with one or more additional impurities selected from thegroup consisting of carbon dioxide, oxygen, nitrogen, water, methane,and mixtures thereof, to produce thereby a purified gas stream; saidapparatus comprising: A. a first reaction zone containing elementalnickel and nickel-carbonyl supported on a carrier selected from thegroup consisting of silicate, titanium silicate and silica; B. means formaintaining said first reaction zone under nickel-carbonyl formingconditions to convert thereby substantially all the carbon monoxide tonickel carbonyl, thereby producing an effluent stream from the firstreaction zone which effluent stream is a partially purified hydrogen gasstream; C. a second reaction zone containing Ti₂Ni; D. means forconveying the partially purified hydrogen gas stream from the firstreaction zone to the second reaction zone; and E. means for maintainingthe second reaction zone under methane reacting conditions to produce apurified hydrogen gas stream.
 2. The apparatus of claim 1, wherein thecarrier has a surface area greater than 100 square meters per gramweight based on the weight of the carrier.
 3. The apparatus of claim 1,wherein the carrier has a surface area greater than 200 square metersper gram weight based on the weight of the carrier.
 4. The apparatus ofclaim 1, where the second reaction zone is a housing with uniformlypolished inner walls having a roughness expressed in a centerlineaverage height less than 0.5 microns.
 5. The apparatus of claim 4, wherethe second reaction zone is a housing with uniformly polished innerwalls having a roughness expressed in a centerline average height lessthan 0.25 microns.
 6. The apparatus of claim 1, where the Ti₂Ni is inthe form of a loose powder having an average particle size of from about1 to about 500 microns.
 7. The apparatus of claim 6, where the Ti₂Ni isin the form of a loose powder having an average particle size of fromabout 1 to about 250 microns.
 8. The apparatus of claim 1, where theTi₂Ni is in the form of pellets having a diameter of about 0.5 to about5 mm.
 9. An apparatus for the removal of gaseous impurities from animpure gas stream of hydrogen contaminated with carbon monoxide, andwith one or more additional impurities selected from the groupconsisting of carbon dioxide, oxygen, nitrogen, water, methane, andmixtures thereof, whereby producing a fully purified gas stream; saidapparatus comprising: A. a first reaction zone containing elementalnickel and nickel carbonyl; B. means for conveying said impure hydrogengas strain contaminated with carbon monoxide, and with one or moreadditional impurities selected from the group consisting of carbondioxide, oxygen, nitrogen, water, methane, and mixtures thereof to thefirst reaction zone; C. means for maintaining said first reaction zoneunder nickel-carbonyl forming conditions thereby convertingsubstantially all the carbon monoxide to nickel carbonyl, therebyproducing an effluent stream from the first reaction zone which effluentstream is a partially purified hydrogen gas stream; D. a second reactionzone containing an alloy of Ti, V, Fe and Mn; E. means for conveying thepartially purified hydrogen gas stream from the first reaction zone tothe second reaction zone; and F. means for maintaining the secondreaction zone under methane reacting conditions to produce a fullypurified hydrogen gas stream.
 10. The apparatus of claim 9, where theweight ratio of Ti:V inside said second reaction zone is from about1:100 to about 100:1.
 11. The apparatus of claim 9, where the weightratio of Ti:Fe inside said second reaction zone is from about 1:100 toabout 100:1.
 12. The apparatus of claim 9, where the weight ratio ofTi:Mn inside said second reaction zone is from about 1:100 to about100:1.
 13. The apparatus of claim 9, further including means formaintaining the pressure in the first reaction zone is about 1 to about20 bar.
 14. The apparatus of claim 9, further including means formaintaining the pressure in the second reaction zone is about 1 to about20 bar.
 15. The apparatus of claim 9, further including means formaintaining the temperature in the second reaction zone is from 400 to600 ° C.
 16. The apparatus of claim 15, further including means formaintaining the temperature in the second reaction zone is from 500 to600° C.
 17. The apparatus of claim 9, where the elemental nickel in saidfirst reaction zone is supported on a carrier having a surface areagreater than 100 square meters per gram weight based on the weight ofthe carrier.
 18. The apparatus of claim 9, where the elemental nickel insaid first reaction zone is supported on a carrier having a surface areagreater than 200 square meters per gram weight based on the weight ofthe carrier.
 19. The apparatus of claim 17, where the carrier isselected from the group consisting of silicate, titanium silicate andsilica.
 20. The apparatus of claim 9, where the second reaction zone isa housing with uniformly polished inner walls having a roughnessexpressed in a centerline average height less than 0.5 microns.
 21. Theapparatus of claim 20, where the second reaction zone is a housing withuniformly polished inner walls having a roughness expressed in acenterline average height less than 0.25 microns.
 22. The apparatus ofclaim 9, where said alloy inside said second reaction zone is in theform of a loose powder having an average particle size of from about 1to about 500 microns.
 23. The apparatus of claim 22, where said alloyinside said second reaction zone is in the form of a loose powder havingan average particle size of from about 1 to about 250 microns.
 24. Theapparatus of claim 9, where said alloy inside said second reaction zoneis in the form of pellets having a diameter of about 0.5 to about 5 mm.